JPS595215A - Lens system having optical system for detecting focal position - Google Patents

Abstract

PURPOSE:To provide a detection system for focal position with high accuracy by making the combined focal length of the entire detection system including a lens for detecting the focal position larger than the combined focal length as the entire system of a lens system for image pickup. CONSTITUTION:A luminous flux splitting element P is provided in a lens system for image pickup, and the luminous flux split by the element P is formed an image by a lens D for detecting focal position. The focal position is detected by measuring the image-forming position thereof. The combined focal length (f) as the entire system of the photographing lens system constituted of a focusing lens F, a zoom part Z and a master lens M and the combined focal length fD of the entire detection system consisting of a lens D for detecting focal position, the lens F and the zoom part Z are so set as to have the relation f<fD.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a detection optical system that improves the accuracy of detecting the focal position in a device that detects the focal position using a light flux that has passed through the photographing lens of a still camera, a movie camera, or a part thereof. Regarding.

Conventionally, a focal position detection system using a photographic lens includes: ■ A focal position detection element is installed on the imaging plane of the lens system or on a plane equivalent to the imaging plane formed by a half mirror placed behind the lens system. ■ A beam splitting element such as a prism block with a half mirror is placed in the lens after the focusing lens part of the lens system, and the focal position vt is equivalent to that of the lens system after the splitting element. , there is one that guides the divided light beam to a detection optical system and forms a detection surface equivalent to the imaging surface to detect the focal position. As a focal position detection element, an element based on image matching (for example, Honeywell's T CL element, etc.) that utilizes a light flux of a specific F1%, or an element that utilizes changes in the 'blur' degree of the image at the focal plane. element (for example, Asahi Optical'r T T,
-E F C, etc.), but K, which both ensures measurement accuracy, is FNIL where the luminous flux concentrated near the element is constant.
must be satisfied.

The above system (■) is often used in -eye reflex still cameras, etc., but when used in a system where focusing and shooting can be separated like this, it is only necessary to stop down after TTL aperture distance measurement, so the exposure The control does not affect the distance measurement accuracy, but is it continuous #4 like a movie camera or video camera? ,
In the case of a system that requires photographing, the luminous flux after exposure control is used to detect the focal position, which is not preferable because exposure control affects detection accuracy.

Therefore, the system (2) is used as a focal position detection system for movie cameras and video cameras, but zoom lenses are often used in these systems, and zoom lenses have optical elements such as half mirrors in their optical systems. This is particularly convenient since it is easy to take up space for distributing flowers.

By the way, conventionally, in the above-mentioned system (2), a detection system consisting of a focusing lens section, a zoom section, and a focal position detection lens section after the beam splitting element, which is common to the camera (11), is as follows:
It was constructed to be equivalent to a zoom lens system, which is an imaging system.

However, the FIt of zoom lenses for movie cameras and video cameras is relatively small, and the screen size is also considerably smaller than that of 35 mm still cameras, so there are the following difficulties.

(2) Since F'NI is small and the screen size is small, the permissible circle of confusion diameter ε is also small, so the focus position detection accuracy δ=10Fε is a small value, and a fairly high focus position detection accuracy is required.

■ The screen size of 8-ray cine cameras and video cameras is small, and the focus position detection element is also required to be small. Using the element developed for existing single-lens reflex cameras as mentioned above, the detection area can be captured easily. The ratio is too high.

For this reason, it has been considered necessary to develop a focal position detection element that is small but highly accurate.

The present invention does not make the focal position detection lens section after the beam splitting element equivalent to the corresponding section of the imaging system, but configures the focal length of the focal position detection lens section to be relatively long,
By enlarging the imaging screen onto the detection element and forming an image, it is possible to enlarge the out-of-focus darkness onto the detection element, thereby solving the above-mentioned difficulty in that the focus position ftIt is 11η on the detection element. This is what was created.

The details will be explained below with reference to the drawings.

Figure 1 shows an afocal zoom lens system that also includes the focusing lens F1 and the zoom section Z.] A master lens M is placed after the afocal zoom system to form an imaging system, and the light beam divided by the half-mirror prism block P after the afocal zoom system is focused. The light is focused onto the cell C by the position detection lens system, and the focal position rf1. An example of the configuration of the detection system is shown below.

where f: Composite focal length of the zoom lens imaging system f': Composite focal length of the zoom lens fish point position detection system fM: Composite focal length of the master lens M! +): the composite focal length of the focal position detection lens system, the following equation holds true.

Here, the distance between object and image changes from infinity to finite t? The focal position deviation scene J of the zoom lens imaging system and the focal position deviation sail δ0 of the focal position detection system when changing to 1li9u are each approximately given by the following equations.

2 δ me...(2) It becomes.

Also, the amount of money the detection element occupies in the screen size is (h/f
D) It is also clear that it will be reduced by a factor of two.

Furthermore, when controlling the 7 focusing lens sections for automatic focus adjustment, fF: composite focal length of the focusing lens δF: positional deviation t of the focusing lens section (controlled amount δ': imaging iI by δF) When the deviation is absorbed by the detection element C plane by δb: δF, the control accuracy of the focusing lens section F is as follows. Not only can the ratio of the area occupied by the distance measurement area on the screen be optimized, but also the control accuracy of the focusing lens section for automatic focusing can be improved, which is a remarkable effect.

In order to specifically demonstrate this, a case will be considered in which it is applied to 4 inotibidigon using a TCL element manufactured by Nornewell.

The size of the 'L' CL element is 5 mm, which is equivalent to the photographing surface of a zoom lens for &inch videocon, so if it is placed as is, the photographic surface of the videocon will be (4.6 x 6.1).
Since it is 2fK, the ratio to the 111th plane is about 82%. It is generally considered that this ratio is preferably 30 to 1°.Also, the permissible internal confusion diameter e of the svidicon is given by the following equation from the vertical length of both sides, 4.6 mm, and the number of scanning lines, 250.

ε = Thin 0.02 (River 50) Therefore, when using a zoom lens of F'! Il & 11.4, the allowable focal shift δ is δ = F$ x s = 1., 4 x 0.02 words 0
．． 03 (Fin) However, the focal position detection accuracy of the TCL system in F4 mode is considered to be approximately ±0.151111. .

In the embodiments shown in the second group, the lens system specifications are shown in the following table when the focal length of the detection system is three times the focal length of the imaging system. Table I shows the Id\rt system, Table 2 shows the focal position detection lens, and Table 3 shows the detection system including the afocal part.

Table 1 Zoom lens photography 1-zoom system focal length f = B, ott ~ 4B, 118F nano (
1,4 pixels f#4 2W=53~8.7 lens 2 Focal length*f269,8: 8 F plano (-4,0 pixels
Angle 2 W = 4.0 degrees/B = 34.415 Table 3 Focal cone resistance f = 23.862 to 143.323 F
Number 4.0/B=34.017 In this example, in equation (3), δD=calculated detection accuracy δ17t δ=±O,] 5/(3+”±0.021F bottle image plane conversion of detection area The area ratio dR = 5/6.1 ÷ 3 words 27%, and a highly accurate solid spot detection system was realized.

Although the above embodiments have been described with reference to a zoom lens having an afocal zoom section, it goes without saying that the same can be applied to a zoom 1/lens or an ordinary single focal length lens system.

[Brief explanation of the drawing]

#￥1 Figure is an optical layout diagram of one embodiment of the optical system of the present invention, p
FIG. 42 is a sectional view of the lens system, and FIG. 3 is an aberration diagram at the detection element surface H. F: Focusing lens Z: Between zoom parts: Master lens D: Focus position Pt detection lens P: Prism with half mirror C: Detection cell No. 1 M

Claims (1)

[Claims] A light beam splitting element is disposed in the imaging lens system, and the light beam split by the element is formed into an image by a focal position detection lens, and the focal position is determined by measuring the image plane position. In the lens system for detection, 1t#fD for the synthetic focus of the entire detection system including the focal position detection lens is f<f with respect to *f for the synthetic focus as the entire system of the IS image lens system. A lens system having a focal position detection optical system characterized by having the following relationship: